The present invention relates, in general, to a method of fabricating a single crystal colloidal monolayer and, more particularly, to a method of fabricating a wide-area single crystal colloidal monolayer in a short time.
Generally, there are attempts to align and structuralize particles such as colloidal particles on a substrate. Here, the particles are required to be aligned in a monolayer over a large area without defects.
Assembled particle monolayers are ordered arrays of uniformly-sized particles. They have long been investigated both theoretically and experimentally. With tunable feature dimensions depending on the particle size, they can be used as lithographic masks to fabricate patterned surfaces with micro- or nanostructures. Their periodic structures have attracted significant interest related to the creation of photonic crystals and optical sensors, antireflective surfaces, superhydrophobic or superhydrophilic surfaces, and self-cleaning surfaces. Recently, the localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) coming from noble metal nanopatterns with high spatial resolutions have been utilized in researches for biosensors, photovoltaics, and light manipulation. A colloidal monolayer can serve as an excellent template for the preparation of ordered metallic nanostructures.
Over the past decades, fabrication of the colloidal monolayers has seen a tremendous amount of success. A variety of processes have been explored to create highly ordered, large-area assemblies. Direct assembly on a target substrate from a colloidal suspension has been the common approach, which includes solvent evaporation on a flat surface, dip-coating, spin-coating, electrostatic and electrophoretic deposition. These approaches using the convective flow request delicate evaporation conditions to obtain a monolayer with large surface coverage. Moreover, cracks are unavoidable due to the decrease in volume while the solvent evaporates. Although self-assembly at the air-water interface allows for the formation of a high-quality, large-area colloidal monolayer without cracks, the preparation of a single crystal monolayer over a large area has been a major challenge. Perfect spatial registry has been attempted with evaporation-assisted deposition on physical templates that were fabricated by conventional lithography or by a wrinkling process. However, this solution-based template approach is slow and sensitive to the evaporation conditions.
Although self-assembled colloidal particles can be widely used, problems arise in that it is not easy to reproduce them and it is difficult to form a monolayer over a large area.